By the mid-1800s, mechanical and optical technology had advanced enough to allow twin telescope binoculars to be produced. By the last quarter of the 19th century, twin telescopes had evolved to very sophisticated optical systems. In some models, the lens system and the mechanical mounting were miniaturized so that twin telescope binoculars could be produced with a length of less than 160 mm. The smallest twin telescope binoculars had objective lenses with aperture diameters of 10-12 mm, and they collapsed for storage to under 120 mm.